Communication networks

ABSTRACT

A communications network comprises a plurality of ports modelled according to a layer protocol, and a network management system adapted to store information describing the physical and logical resources within the network, wherein the network management system is responsive to information describing connectivity in a first one of the layers to derive further information concerning connectivity in another of the layers. The first layer is preferably the closest known layer connectivity to the physical layer and the derived connectivity information applies to successive ones of the upper layers.

FIELD OF THE INVENTION

The present invention is concerned with communication networks, morespecifically with certain control/management aspects of such networks.

BACKGROUND TO THE INVENTION

A conventional communications network, for example a broadbandcommunications network, comprises a plurality of physical resources inthe form of network elements, eg switches, cross connects, regenerators,repeaters, transmission links such as fiber optic links or coaxial cablelinks, operating under control of a plurality of logical resources, egtransport protocols, and local controls associated with individualphysical resources. An example of a generic representation of acommunications network is illustrated schematically in FIG. 1, in whichthe physical resources of a core network are located at a plurality ofnodes 100 and links 101 distributed over a geographical area.

For a network operator to maintain control of a communications networkfor its operation, administration and maintenance, a management systemis maintained which stores information describing the physical andlogical resources within the network. One or more management systems mayreside at a centralized location, eg a network controller 102, ordifferent management systems may be situated at a plurality of networkcontrollers at different locations. The management system stores datadescribing each individual network element in a communications networkand has one or more management applications which use the data to managevarious aspects of the network, eg operation, administration, andmaintenance of the network.

A conventional communications network may comprise of the order ofthousands of individual network elements, eg switches, cross connects,regenerators, each of which contains of the order of tens to hundreds ofcards, having processors, line terminations, buffers, registers, switchfabrics, etc. each card containing of the order of hundreds ofindividual components. In general, a conventional communications networkmay comprise a multitude of different legacy equipment types ofdifferent proprietary manufacture, each of which has its own particularinternal configuration and offers its own specific capabilities.

International Telecommunications Union (ITU-T) recommendation G.805 ofNovember 1995, (available from International Telecommunication Union,General Secretariat, Sales Service, Place de Nation, CH 1211, Geneva 20,Switzerland), sets out a functional architecture for telecommunicationstransport networks in a technology independent manner. A genericfunctional architecture is set out as a basis for a harmonized set offunctional architecture recommendations for broadband transport networkincluding asynchronous transfer mode (ATM), synchronous digitalhierarchy (SDH) and plesiochronous digital hierarchy (PDH), as well as acorresponding set of recommendations for management, performanceanalysis and equipment specification for such transport networks.

In general, in known transport networks circuit switched communicationsare made on an end-to-end basis over a plurality of network entities. Inthis specification, by circuit switched, it is meant that the networkreserves part of its resources for the purpose of supporting anend-to-end communication, for the duration of that communication,whether those resources are used or not.

Referring to FIG. 2, there is illustrated a simple example of a trail ofa circuit switched communication over part of a communications transportnetwork. A trans-port network is defined in recommendation G.805 as “thefunctional resources of the network which conveys user informationbetween locations”. In recommendation G.805, a trail is defined as “atransport entity which consists of an associated pair of unidirectionaltrails capably of simultaneously transferring information in oppositedirections between their respective inputs and outputs”. Aunidirectional trail is defined as a “transport entity” responsible forthe transfer of information from the input of a trail termination sourceto the output of a trail termination sink.

The integrity of the information transfer is monitored. It is formed bycombining trail termination functions and a network connection. Atransport entity is defined as “an architectural component whichtransfers information between its inputs and outputs within a layernetwork. A layer network is defined as “a topological component thatincludes both transport entities and transport processing functions thatdescribe the generation, transport and termination of a particularcharacteristic information. A connection is defined as “a transportentity which consists of an associated pair of uni-directionalconnections capable of simultaneously transferring information inopposite directions between their respective inputs and outputs. Auni-directional connection is defined as “a transport entity whichtransfers information transparently from input to output”.

In FIG. 2, there is illustrated schematically a plurality of transportentities 200, 201, 202, 203, 204 in a communications network comprisingnetwork elements eg switches, cross connects, links, supporting an endto end trail between first and second trail termination points 205, 206.The trail is carried over a plurality of connections which connect thetransport entities to each other. Connections between transport entitiesterminate at a plurality of connection termination points (CTP) withinthe trans-port entities.

The generalized trail as illustrated in FIG. 2, incorporates differenttrails in different transport protocols. For example, virtual paths andvirtual circuits in asynchronous transfer mode (ATM) constitute trailswithin the meaning of ITU-T Recommendation G.805. ATM cells may becarried within a virtual path within SDH frames over an SDH trail.

Within a layered network, protocol trails occur within layers. Trailscan occur at a plurality of different layers. However, each trail isalways contained within its own layer. In a large network, comprisingtens to hundreds of network elements, management of end-to-end trailsposes a highly complex problem and poses difficulties in the practicalimplementation of setting up and tearing down of trails. The concept oftrail management is mentioned in recommendation G.805 in which a trailmanagement process is defined as “configuration of network resourcesduring network operation for the purposes of allocation, reallocationand routing of trails to provide transport to client networks.”

Conventionally, for creating a trail across a network it is known forseveral network operators, at several network controllers controllingdifferent sections of the network, to each set up one or moreconnections within sections of the network which they control. Toachieve a trail over a large number of transport entities, a networkoperator wishing to set up a trail may need to contact, by means of atelephone call or a fax, other network operators having control of otherparts of the network across which a trail may pass, and co-ordinate thesetting up of a trail by verbal or fax communication with the otherhuman network operators.

In conventional prior art network management systems, it is known tokeep a master database which always overwrites whatever connectionsexist in the real network under management. Thus, if a network operatormakes changes to connections or trails in a network by configuring anindividual network element directly, the conventional network managementsystem database will attempt to overwrite any changes made at thenetwork element level, regardless of whether the network operatorintended those changes to the network element or not. Further, the knownnetwork management systems do not provide an ability to drawconfiguration and connectivity information from the real network and donot compare such information with the information kept in the masterdatabase.

Prior art network management systems either represent networkconfigurations which a network operator plans at a network controller,and implements those configurations irrespective of existingconfigurations of a network, or provide a network operator with datadescribing actual network configurations, without taking into account ormaking provision for a network operator's planned or intended presentand future configurations of the network.

In the following discussion, a preferred implementation of the inventionis described with reference to synchronous digital hierarchy (SDH)systems. However, it will be understood that the scope of the inventionis not restricted to SDH systems but extends over any network ofphysical and logical resources in the telecommunications or computernetworks domains having a management information system,

Networks operating asynchronous transfer mode (ATM), synchronous opticalnetwork (SONET), integrated service digital network (ISDN) and SDH arespecific examples of such networks. However, the invention is notrestricted to networks operating these specific protocols.

ITU-T recommendation G.803 deals with the architecture of SDH transportnetworks and defines an SDH based transport network layered model asillustrated in FIG. 3. The G.803 model uses a functional approach to thedescription of architectures based on the concept of a number of SDHfunctional layers and the concept of partitioning within a layer fordefining administrative domains and boundaries.

Physically, a conventional SDH network is constructed from a pluralityof physical resources, for example network elements such as exchanges,multiplexers, regenerators, and cross connects. The network elements areconnected together and provide a transmission media layer, including asection layer comprising multiplex section layer 300, a regeneratorsection layer 301 and a physical media layer 302. Circuit switchedtraffic is routed over the physical resources in a circuit layer 303which is carried by the SDH transport layers.

The SDH multiplexing structure is illustrated schematically in FIG. 4,which also shows synchronous optical network (SONET) multiplexingoptions and European Telecommunications Standards Institute (ETSI)multiplexing options. The SDH transport layers comprise, in addition tothe physical media layer and section layer, a plurality of higher orderpath layers, for example carried by virtual containers VC-3, VC-4, and aplurality of lower order path layers, for example carried by virtualcontainers VC-2, VC-3, VC-11, and VC-12.

Data is carried between network elements which are geographicallyseparated by large distances at relatively high data rates, eg 155Mbits/s. Circuit switched connections, referred to as a circuit layer301 in recommendation G.803, are transported across the SDH network byencapsulating bit streams comprising the circuit switched connectionsinto different virtual containers (VCs) which are multiplexed togetherfor transmission at higher order bit rates.

Within the physical resources, circuit switched traffic follows pathsand trails at various multiplex levels. Connections are terminated atconnection termination points (CTPs), and trails are terminated at trailtermination points (TFPs) within physical resources. For example, withina communications network, there may be a restricted number of networkelements which are capable of processing voice data.

Operations on voice data at a voice level may be performed within thoseparticular network elements. However, to transport traffic data betweenthose network elements, there must be further transmission, such asprovided by the SDH virtual container system. Thus, where a voiceconnection is to be made between geographically disparate networkelements A and B, the connection may be routed via intermediate networkelements D, E, F, G etc which may be in the VC-12 layer. However, theVC-12 layer itself, to connect between intermediate network elements E,F, may need to be multiplexed into a higher bitrate layer, eg the VC-4layer.

Referring to FIG. 5, there is illustrated schematically a section of anSDH communications network comprising a plurality of network elements500-505 operating under control of an element controller 506 and managedby a network controller, referred to herein as network resource manager507.

The element controller communicates with the plurality of networkelements via an operations administration and control channel 509, egusing a conventional network management protocol, for example the knowncommon management information service element (CMISE) protocol. Theelement controller communicates with the network resource manager 507via a conventional protocol, for example the transmission controlprotocol/internet protocol (TCP/IP) over a transmission link 508. Thenetwork resource manager 507 implements control of the network byimplementing operations, administration and management operations of thenetwork elements, through one or a plurality of element controllers 506.

Referring to FIG. 6, there is illustrated schematically the constructionof a typical network element 600, element controller 506 and networkresource manager 507. Network element 600, for example a multiplexer orcross connect, comprises a casing or cabinet having one or a pluralityof shelves, each shelf containing a plurality of cards 601. The cardscontain processors, switch fabrics, line terminations etc depending uponthe type of network element, and are connected to each other via a databus. In the case of an SDH multiplexer, each card may support a numberof physical ports. Each port supports a plurality of connections. Thenetwork element is provided with a local control system 602 comprising adata processing capability configured to send and receive messages overthe CMISE OAM channel 509.

The element controller comprises a workstation 603, for example aHewlett Packard 9000 series workstation comprising a processor 604, adata storage device 605, a bus 606 linking the processor and datastorage device, a graphical user interface 607, and a communicationsport 608 for communicating with the network element and the networkresource manager. Typically, the element controller operates accordingto a UNIX operating system 609.

The network resource manager 507 similarly may comprise a work station610, eg Hewlett Packard 9000 series having processor 611, memory 612,bus 613, graphical user interface 614 and communications ports 615components, operating in accordance with a UNIX operating system 616.The network resource manager and the element controller are configuredto communicate with each other using for example TCP/IP link 508.

The network resource manager comprises a managed object base (MOB) 617containing data describing characteristics and configurations of thenetwork elements under its management. Within the net work resourcemanager, each network element is represented as a managed object, inaccordance with the telecommunications network management network (TMN)architecture of ITU-T recommendation M.3010.

In managed object base 617 physical resources of the network, comprisingthe transport entities supporting the trails, eg central officeswitches, multiplexers, regenerators, cross-connects etc are representedas managed objects according to ITU-T recommendation M.3010 (Principalsfor a Telecommunications Management Network) in known manner.Additionally, individual capabilities and functionalities of thosephysical resources, for example trail termination points, connectiontermination points and adaptations within individual physical or logicalports of the physical resources, and the connection limitations andconnectivity capabilities of those physical resources are representedwithin managed object base 617 according to an object representationscheme as disclosed in co-pending U.S. patent application Ser. No.09/010,387 (corresponding to EP 98306103.7) entitled “CapabilityModelling Using Templates in Network Management System”.

The network resource manager 507 comprises a trail manager application620 for managing trails across the network. Management operationscontrolled by trail manager application 620 are implemented at each of aplurality of element controllers 506 by respective trail managementoperation controller server 619. In the specific implementationaccording to the present invention, trail manager application 620provides a network operator with means for managing trails across anetwork. In order to enable an operator to manage trails, trail managerapplication 620 is provided with functionality for:

-   -   planning trails across the network;    -   learning about actual existing trails within the network;    -   storing data describing existing trails within the network        provisioned from planned trails; and    -   storing data describing whether a planned or provisioned trail        is intended within the network.

Within a communications network, although a network operator may createand manage trails using trail management application 620, actual trailsmay exist within the network which are different to those which thenetwork operator has intended. Trail management application 620 isprovided with a graphical user interface (GUI) 614 which enables thenetwork operator to view both the actual trails within the network andthe network operator's planned and/or intended trails within thenetwork. For each trail under management of the trail managementapplication 620, there is maintained data representing a status of thetrail. The means for representing the status of each trail comprises astate machine which is part of the trail manager application 620,providing data to the trail manager application.

The state machine comprises data processing capability and data storagecapability (a database) for maintaining and processing data describingone or more states of each trail under management. In the specificimplementation herein, the state machine is physically implemented byconfiguration of the processing and data storage capabilities of theconventional network management system, for example one or more HewlettPackard 9000 Series Workstations configured as the element controller,and network resource manager as illustrated in FIG. 6.

Such configurations are implemented by arrangement and allocation of adata storage device and by provision of a set of algorithms to performdata processing operations on data stored on the database. Sucharrangements and algorithms may be implemented in a conventionalprogramming language, such as the known C/C⁺⁺ language as will beappreciated by those skilled in the art. Specific programming optionsand variations of implementations are numerous and will be readilyapparent to the skilled person.

The trail manager 620 obtains data describing specific trail terminationpoints within individual network elements, from managed object base 617,as described in the aforementioned co-pending patent application, and isthereby provided with information concerning available capacity andconnection capabilities for supporting trails and connections. The trailmanager application 620 obtains data describing the capabilities,including connectivities and restrictions on connectivities of each ofthe network elements by referencing a set of data templates stored inthe managed object base. The templates include templates describingphysical or logical ports of a network element, together with connectiontemplates describing possible connectivities of termination pointswithin each physical or logical port of a network element on a layer bylayer basis.

A simple example of an aspect of trail management within a network willnow be described with reference to FIGS. 7 to 10, which illustrateschematically a representation of an SDH trail traversing three networkelements 700, 701, 702. For example, the trail may comprise a VC12trail. VC12 payloads may enter the trail at trail termination sourcepoint 703 and is output at trail termination sink point 704. Trailtermination is defined as a “transport processing function” thatconsists of a co-located trail termination source and sink pair. A trailtermination sink is defined as a “transport processing function” whichaccepts the characteristic information of the layer network at itsinput, removes the information relating to “trail” monitoring andpresents the remaining information at its output. A trail terminationsource is defined as a “transport processing function” which acceptsadapted “characteristic information from a client layer network at itsinput, adds information to allow the “trail” to be monitored, andpresents the characteristic information at its output. The trailtermination source can operate without an output from a client layernetwork. The trail is supported by a plurality of connections 705, 706between the network elements which enter and leave the network elementsat VC12 connection termination points (VC12 CTP) 707-710. The VC12 trailoccurs within a VC12 layer, and the connection termination points occurwithin that layer.

The connection termination points comprise transit points within thetrail, between network elements supporting the VC12 layer. Virtualcontainers traverse the connection termination points without beingde-multiplexed. Routing of the VC12 containers is not dependent upontheir content, but is dependent upon the path or route taken by thetrail across the network elements. At trail termination sink point 704,the VC 12 container payloads may be de-multiplexed, eg to a plurality of2048 Kbits/s streams. Sub-network connections 711, 712, 713 determineconnectivity within the network elements from input connectiontermination points of the network elements to output connectiontermination points of the network elements.

In general, each port supporting a trail is represented by a column oflayers, as illustrated in FIG. 8. Depending upon the protocol layerssupported by the ports, the height of the column may differ from port toport. FIG. 8 illustrates schematically a data representation of part ofthe VC-12 trail over network elements 700, 701 as stored in the managedobject base 617. For each network element, a physical or logical portsupporting the trail is represented as an assembly of termination pointdata templates 900, represented by symbols as illustrated in FIG. 9.Symbol 901 represents a trail termination point, symbol 902 representsan adaptation between a same layer of the trail termination point and aclient layer, symbol 903 represents connectivity to a client layer, andsymbol 904 represents connectivity to other termination points in thesame layer.

In FIG. 8, a trail, eg a VC-12 trail, enters first network element 700at VC-12 termination point 703 through VC-12 adaptation 800 at a firstport 801 of first network element 700. Transport between first andsecond network elements over link 705 is effected over SDH physicalmedia section 802 to an entry port 803 of second network element 701.Conversion of the physical media section through the SDH protocol layeris represented by a set of data templates representing the physicalmedia section layer 802, optical section layer 805, regenerator sectionlayer 806, STM-N layer 807 and HP-VC4 layer 808 each represented by aseparate data template as illustrated in FIG. 9. Internal connectionsbetween input and output ports 803, 804 within same network element 701are made via a VC-12 connection 712.

Referring to FIG. 10, a trail 1000 between trail termination sourcepoint 703 and trail termination sink point 704 may be set up by anetwork operator at network resource manager 506, similarly as describedin FIG. 7. The trail manager 620 has a record of the actual trail in thenetwork from data read from managed object base 617, in accordance withthe data template representations described with reference to FIGS. 8and 9. However, in the network, the actual trail may become altered fromthat created or intended by the network operator, for various reasons.For example, maintenance personnel may be able to take local control ofnetwork elements in order to reconfigure connections directly at thenetwork element level, overriding the network resource manager 506 andelement controller 507. Thus, in this example in practice an actualtrail may be reconfigured, due to local alterations made at secondnetwork element 701 so that the VC-12 trail is re-routed to a fourthnetwork element 1001 as shown in FIG. 10. Thus, a new actual trailexists in the network between second trail termination source point1003, through fourth network element 1001, second network element 701,and third network element 702 to end at trail termination sink point704. Therefore, whilst a network operator at network resource manager507 intends a first trail between first and third network elements asshown in FIG. 7, due to external circumstances beyond the networkoperator's control, eg due to local reconfiguration of second networkelement 701, an actual trail between fourth and third network elementsmay be created as illustrated in FIG. 10, which is different to theintended first trail, and overwrites it.

In many cases, the actual trails within the network are the same astrails intended by the network operator. However, discrepancies betweenintended and actual trails do occur. To provide comprehensive trailmanagement throughout the network, the state machine keeps a record of:

planned trails, eg as input by a network operator at GUI 714 of networkresource manager 507; and

actual trails within the network, eg created at network resource manager507 and provisioned in the network, or as a result of events occurringwithin the network independently of network resource manager 507 andelement controller 506.

Planned and actual trails may either be intended or unintended. Usually,the intention of a network operator is that all trails planned at thenetwork resource manager 507 become executed as actual provisionedtrails in the network. However, trails which were not planned at thenetwork resource manager may or may not be intended.

In the case of the example of FIG. 10, trail manager application 620records the actual trail 1002 between fourth and third network elements,the intended trail 1000 between first and third network elements, andthe fact that the actual trail between fourth and third network elementsmay also be intended (since it is a valid trail). Additionally, thestate machine may record data representing that each trail identified inFIG. 10 is a valid trail and that they are in conflict: that is to sayboth trails cannot exist at the same time in the network, because theyare mutually exclusive in terms of their demands on the networkelements, as well as recording which of the trails was originallyplanned, and which of the trails has been learnt from interrogation ofthe network, and may indicate that the trail manager application 620cannot resolve the discrepancy between the two trails.

The state machine maintains one or more state models for each trailunder management of the trail manager 620. The trails may be eitheractual trails existing within the network or trails intended to becreated or having been created by the network operator. A state modelcomprises a data record of a trail which records a state in which thetrail currently resides, ie a condition of the trail.

The data is held in a database containing a list of trails within anetwork, together with data describing a status and characteristics ofthe trail according to a state model. For each trail there is maintaineddata describing the trail in managed object base 620 in the form of oneor a set of trail objects. The state machine performs automaticoperations on the trail objects, depending upon which one of a pluralityof possible states they reside. Further, a network operator may activateoperations on the trail objects, eg by typing in commands at graphicaluser interface 614.

Previous approaches to dealing with network management problems haveincluded solutions at opposite extremes, namely (i) not modelling thelayered network correctly (typically by omitting layers) and (ii)requiring the customer or network devices to provide much moreinformation. The former approach has a deleterious effect on the abilityof the network management system to fulfil its function. For example,network service fault correlation is impeded since the layered model isincomplete. The latter approach is impractical since customers or thenetwork devices do not normally have access to the necessary data.Moreover, detailed knowledge of the network is required in advance andvast quantities of customer input is required. This necessitates a hugeamount of data collection and continuous customer amendments withchanges to the network. This is in addition to the undesirability ofpassing part of the burden of network management on to the customer,thereby diminishing the appeal of the network to the customer. Theseproblems usually mean that there really is no viable alternative andnetwork management of a multi-layered network is not viable.

SUMMARY OF THE INVENTION

In general terms, the present invention provides a method, acommunication network and a network management system incorporating atechnique by which management of the network is assisted, or in someinstances made possible, by deriving information already available incertain layers/protocols of the network, for example from informationabove the server layers.

In a first aspect, the invention provides a communication networkcomprising a plurality of ports modelled according to a layer protocol,and a network management system adapted to store information describingthe physical and logical resources within the network. The networkmanagement system comprises means responsive to information describingconnectivity in a first one of the layers to derive further informationconcerning connectivity in another of the layers.

The invention also provides a method of managing a communication networkcomprising a plurality of ports modelled according to a layer protocoland a network management system adapted to store information describingthe physical and logical resources within the network. The methodcomprises utilising information describing connectivity in a first oneof the layers to derive further information concerning connectivity inanother of the layers.

The invention further provides a network management system adapted tostore information describing the physical and logical resources within acommunication network comprising a plurality of ports modelled accordingto a layer protocol. The network management system comprises meansresponsive to information describing connectivity in a first one of thelayers to derive further information concerning connectivity in anotherof the layers.

The invention yet further provides a method of operating such a networkmanagement system. In addition, the invention provides software enablinga computer to operate the above method and manage the above system andfurther provides storage media storing the software.

In all cases, the said first layer is preferably the closest known layerconnectivity to the physical layer of the modelled communicationnetwork.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the drawings, inwhich:

FIG. 1 is a generic representation of a communications network in whichthe present invention may operate;

FIG. 2 is a simple example of a trail of a circuit switchedcommunication over part of a communications transport network;

FIG. 3 illustrates an SDH based transport network layered model;

FIG. 4 illustrates an SDH multiplexing structure;

FIG. 5 illustrates schematically a section of an SDH communicationsnetwork;

FIG. 6 illustrates schematically the construction of a typical networkelement;

FIG. 7 illustrates schematically a trail across a plurality of networkentities within a communication network as in FIG. 5;

FIG. 8 illustrates schematically a plurality of ports comprising networkelements in the network of FIG. 5;

FIG. 9 illustrates schematically a data representation of a trailtermination point and adaptation functionality corresponding to FIG. 8;

FIG. 10 illustrates schematically a planned trail and an actual trailwithin a communication network;

FIG. 11 is a schematic illustration of the levels of link, linkconnection and trail between network elements;

FIG. 12 is a schematic illustration of model packaging used in thepresent invention;

FIG. 13 depicts a trail model scenario as an exemplary implementation ofthe invention;

FIG. 14 is a schematic illustration of the first step of the trailmodelling scenario illustrating the present invention;

FIG. 15 is a schematic illustration of the second step of the trailmodelling scenario illustrating the present invention; and

FIG. 16 is a schematic illustration of the third step of the trailmodelling scenario illustrating the present invention;

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In the following description of the best mode of implementing theinvention, reference to the most common layer protocols outlined in theintroduction will be made in the context of putting the invention intopractice in a preferred mode, representing a particular approach to thenetwork management solution.

In this approach, the invention enables a network management systemmodelling a communication network to derive trails, links and linkconnections present in the network at various layers/protocols fromminimal information available to it. The invention incidentally alsoprovides end-to-end compatibility checking which assists in theverification of connectivity validation.

In the exemplary communication network described above with reference toFIGS. 1 to 5, there are numerous layers of transmission at work, eachensuring transport of a particular characteristic information. This maytypically be individual protocols. The connectivity within thecommunication network is numerous and complex. Moreover, there are manyprotocols involved.

Circumstances arise in which the network management system obtainsinformation about the connectivity in one such layer/protocol. Theinvention permits this information to be used, in conjunction withknowledge of the function and capability of the equipment involved inthe connectivity to derive much more connectivity informationautomatically, without the need for data collection and input by thecustomer or the network devices.

Consider, for example, the situation where a network port is connectedto an optical fibre. Information concerning the connectivity of thatport will be stored in the network management system. To be morespecific, if the communication network is one that operates bymaintaining a database of templates representing the connectivity ofeach and every port within the communication network, certainconnectivity information will be represented in the template for thatport.

Reference may be had to U.S. Pat. No. 6,223,219 for a detailedexplanation of the template approach.

From the information stored in the template and from informationconcerning the equipment capability, further information concerningconnectivity (eg trails, links, link connections) in the Optical Section(OS), Regeneration Section (RS), Multiplexer Section (MS), multiplexersection protection and partial High Order (HO) & LO path can be derived.The invention is not limited to these layers. For example, if theequipment is DWDM capable, the OTS, OMS, OCH and DSR layers can besimilarly derived.

In one preferred method for deriving such further information, thenetwork management system is provided with information concerning thefunction and capability of the ports/connections points and connectivitymatrices of the equipment involved in connectivity. The networkmanagement system utilises this information to analyse the knownconnectivity and thereby to predict or infer network services that maybe available in client layers and hence generate client links.

This capability information can further be used to understand whatactually happens when a layered network is offered a network service, iea link, by the server layer. This sometimes means that the intra-layerconnectivity represented in the matrix corresponding to the device inquestion connects, terminates and adapts the offered signal in such away that a further end-to-end transport is provided in the layerednetwork.

This analysis continues recursively over the layer network. It can then“ripple” over and through a port/termination point and off to anotherconnected device where the analysis continues to recurse. In this way,implied trails, links and link connections can be implied at potentiallymany client layers.

Referring now to the preferred mode or implementation of the invention,it will be recalled that each layer of a hierarchical network, such asG.805, represents a protocol, perhaps better described as acharacteristic information. This representation has already beenoutlined in the introduction. In each layer, the trail termination point(TTP) extracts a header from data whereas the adaptation function“understands” what needs to be done with the content.

Consider then the situation illustrated in FIG. 12. At a certain instantin time, a trail may exist between the trail termination points of nodesor Network Elements (NEs) identified as A and B in the network. The linktermination point for NEA is located immediately at the top of theadaptation part 902 of the model shown by FIG. 9. It defines the layerboundary between the server layer SL and the client layer CL. Trails aremodelled between the TTPs of the ports or NEs. In similar manner,“links” are modelled between the link termination points (LTPs) at thelayer boundary.

When a trail and a link have been established, a link connection LC isestablished between the connection termination points (CTPs) on theconnection function 903 (FIG. 9) between different ports/NEs. The linkis actually created by looking at the header(s) in the client overheadand allocating an appropriate link to represent capacity at the clientlayer. Where a client overhead contains more than one header, each withits own overhead, thereby implying more than one link, the link hascapacity greater than one and each of these client capacities can beallocated to a link connection.

It is important to remember that, in hierarchical/topological modelling,the lower order client layer networks use transport services provided byunderlying, higher order, server layer networks. Therefore, connectivityat a lower layer can only be supported by connectivity at a higherlayer. Within a layer, a plurality of subnetworks can exist, the largestpossible sub-network being the layer itself. When this situation exists,the sub-networks are interconnected by links. Links can be considered asrepresenting the potential for bandwidth or the trail in the clientlayer.

The transport processing functions necessary to transport a signalacross the network require the three aspects of adaptation, terminationand connection, as shown previously in FIG. 9. (This figure is in fact asimplification of the G.805 model, which is otherwise identical exceptfor the provision of an “access point” between the termination andadaptation functions.) It is worth noting that the adaptation functionpasses a collection of information between layer networks by changingthe way in which the information is presented. In particular, it isresponsible for:

Client encoding—adaptation source adapts a data stream into the servercharacteristics;

Client labelling—adaptation source labels each client so that thecorresponding adaptation sink can correctly identify it (also enablesmultiplexing);

Client alignment—adaptation source aligns the client signal with thecapacity in the server layer.

In general terms, the Trail Termination Function generates, adds andmonitors information concerning the integrity and supervision of theadapted signal, whilst the Connection Function relays a collection ofitems of information between termination points. It does not modify themembers of this collection of items of information, although it mayterminate any switching protocol information and act upon it. TheConnection Function is the same topological component as theSub-network. Connections across the Function are Sub-networkConnections.

The functions of the various termination points mentioned in thepreceding paragraphs can be summarised as follows:

Trail termination point (TTP)—encapsulates a (G.805) terminationconnection point and a transport processing function that penetrates thecharacteristic information of a layer network and ensures the integrityof that characteristic information;

Link termination point (LTP)—represents the server layer TTP in thecharacteristics of the client layer encapsulating the server adaptationcapacity in the form of CTP potential; and

Connection termination point (CTP)—encapsulates a (G.805) connectionpoint which is capable of transparently connecting the clientcharacteristic information through a subnetwork connection (SNC) or alink connection.

Thus far, topological entities have been considered in the logicaldomain. However, they can be packaged together with their physicalequipment counterparts. In this “model packaging” there are threetransport equipment entity types that are key to the network solution,as follows:

Managed element (ME)—describes a discrete network entity having a set ofmonitored and/or controlled transport processing and support functionsimplemented by physical ports and matrix capabilities. It must beco-located and geographically inseparable;

Endpoint—describes the location and existence of a physical or (rarely)logical or port pair; and

Managed Object Agent (MOA)—acts as the network management contact pointfor information about the physical and logical resources within itsdomain of control.

Network elements (NEs) contain endpoints representing physical ports,each of which has a logical presence in a number of layer networkdomains and subnetworks. FIG. 12 represents an optical port package, a2M tributary port and a 2M tributary port cross-connected to an STM-1optical port using the LO VC-12 layer.

For the purposes of the present embodiment of the invention, the twotributary ports are of significance. In each case, the connectionfunction represented by the ellipse at the top of each port indicatesconnection into another port to a different subnetwork via a trail/link.

The Figure illustrates how the network elements contain endpointsrepresenting physical ports, each of which has a logical presence in anumber of layer network domains and sub-networks. Each template of theconnection, adaptation and termination functions has rules governing themanner in which connections and functions can legally be made. Thus, inthe client layer, there will be client connection rules associated withthe connection function. Similarly, there will be TTP rules governingtrail termination point connection.

For example, consider the situation where a TTP template might representa VC4 layer TTP that is restricted by hardware limitations to produceonly VC3 and VC12 but not VC11. The adaptation rules would thenexplicitly state the adaptation capability and would identify only VC3and VC12. Each time a TTP with these properties was “installed” in anNE, a message identifying the TTP template would be issued by the EC.There will not normally be a large number of templates required becausevendors usually have a restricted variety of TTPs in their portfolio.

Consider now a scenario in which it is required to model a real networkin which Network elements A and C are to be connected through networkelement B, as illustrated schematically in FIG. 13. When a trail isbeing laid, the first operation is to define the physical connectivitybetween ports. As can be seen in FIG. 14, the trails, links and linkconnections work their way up the hierarchy from the physical layer PMSaccording to the connection rules. In this particular case, the “mustconnect” rule causes auto client propagation up the hierarchy until thefirst flexible layer (VC4) is reached.

At this point, the VC4 connectivity between NEA and NEC is defined, asrepresented in FIG. 15. In this particular scenario, NEB is assumed tocontain a passthrough CTP-CTP SNC, whilst NEA and NEC terminate the VC4.

In the final step, illustrated schematically in FIG. 16, the LO VC12trail is established between NEA and NEC. By having built upwards inthis way from the physical connectivity to the Virtual Container layers,connection to other subnetworks becomes modelled and the trail iscomplete. It can therefore be seen that in the method, the trail“ripples” up the hierarchy.

An example of pseudocode to enable the invention to be achieved wouldinclude the following:

Build a link from the information supplied Point A: For each possiblechannel on the link, Create an empty trail route structure For each endon the link, Follow the MustConnect connection rules/existingconnections and underlying links, inserting the details into the trailroute structure, until a trail end is found If the trail route structuredescribes a complete trail Build the trail using the route Build clientlinks on the trail using the intersection of capabilities of all thetrail ends For each link built, recurse to point A

1. A communications network comprising a plurality of ports modelledaccording to a layer protocol, and a network management system adaptedto store information describing the physical and logical resourceswithin the network, wherein the network management system is responsiveto information describing connectivity of ports in a first one of layersof the layer protocol to derive further information concerningconnectivity of ports in another of the layers, and wherein the networkmanagement system uses information concerning connectivity in the layerprotocol, in conjunction with information describing the physical andlogical resources within the network, to predict or infer networkservices available in client layers.
 2. A communications network asclaimed in claim 1, wherein said first layer is the closest known layerconnectivity to the physical layer of the layer protocol.
 3. Acommunications network as claimed in claim 2, wherein said networkmanagement system is adapted to derive further information in aplurality of successive layers of the layer protocol.
 4. A method ofmanaging a communications network, the network comprising a plurality ofports modelled according to a layer protocol and a network managementsystem adapted to store information describing the physical and logicalresources within the network, the method comprising the steps ofobtaining information describing connectivity of ports in a first one oflayers of the layer protocol; deriving further information concerningconnectivity of ports in another of the layers; and using informationconcerning connectivity in the layer protocol, in conjunction withinformation describing the physical and logical resources within thenetwork, to predict or infer network services available in clientlayers.
 5. A method according to claim 4, wherein the step of obtaininginformation describing connectivity in the first one of the layers isperformed in the closest known layer connectivity to a physical layer ofthe layer protocol.
 6. A method according to claim 4, wherein the stepof deriving information concerning connectivity of ports at another ofthe layers derives information concerning the connectivity of ports of aplurality of the other layers.
 7. A communications network managementsystem having a store arranged to store information describing thephysical and logical resources within a communications network, thenetwork comprising a plurality of ports modelled according to a layerprotocol, wherein the network management system is responsive toinformation describing connectivity of ports in a first one of layers ofthe layer protocol to derive further information concerning connectivityof ports in another of the layers, and wherein the network managementsystem uses information concerning connectivity in the layer protocol,in conjunction with information describing the physical and logicalresources within the network, to predict or infer network servicesavailable in client layers.
 8. A communications network managementsystem according to claim 7, wherein said first layer is the closestknown layer connectivity to a physical layer of the layer protocol.
 9. Acommunications network management system according to claim 7, furtherarranged to derive said further information for a plurality of otherlayers of the layer protocol.
 10. A method of operating a communicationsnetwork management system adapted to store information describing thephysical and logical resources within a communications network, thenetwork comprising a plurality of ports modelled according to a layerprotocol, the method comprising the steps of obtaining informationdescribing connectivity of ports in a first one of layers of the layerprotocol; deriving further information concerning connectivity of portsin another of the layers; and using information concerning connectivityin the layer protocol, in conjunction with information describing thephysical and logical resources within the network, to predict or infernetwork services available in client layers.
 11. A method according toclaim 10, wherein the step of obtaining information describingconnectivity of ports in the first one of the layers is performed in theclosest known layer connectivity to a physical layer of the layerprotocol.
 12. A method according to claim 10, wherein the step ofderiving information concerning connectivity of ports at another of thelayers derives information concerning the connectivity of ports of aplurality of the other layers.
 13. A computer readable media storingprogram code enabling a computer to perform the method of managing acommunications network, the network comprising a plurality of portsmodelled according to a layer protocol and a network management systemadapted to store information describing the physical and logicalresources within the network, the method comprising the steps of:obtaining information describing connectivity of ports in a first one oflayers of the layer protocol; deriving further information concerningconnectivity of ports in another of the layers; and using informationconcerning connectivity in the layer protocol, in conjunction withinformation describing the physical and logical resources within thenetwork, to predict or infer network services available in clientlayers.
 14. A computer readable media storing program code enabling acomputer to perform the method of operating a communications networkmanagement system adapted to store information describing the physicaland logical resources within a communications network, the networkcomprising a plurality of ports modelled according to a layer protocol,the method comprising the steps of: obtaining information describingconnectivity of ports in a first one of layers of the layer protocol;deriving further information concerning connectivity of ports in anotherof the layers, and using information concerning connectivity in thelayer protocol, in conjunction with stored information describing thephysical and logical resources within the network, to predict or infernetwork services available in client layers.
 15. A computer programproduct comprising a computer readable media storing program code which,when run on a computer, causes the computer to perform the method ofmanaging a communications network, the network comprising a plurality ofports modelled according to a layer protocol and a network managementsystem adapted to store information describing the physical and logicalresources within the network, the method comprising the steps of:obtaining information describing connectivity of ports in a first one oflayers of the layer protocol; deriving further information concerningconnectivity of ports in another of the layers; and using informationconcerning connectivity in the layer protocol, in conjunction withinformation describing the physical and logical resources within thenetwork, to predict or infer network services available in clientlayers.
 16. A computer program product comprising a computer readablemedia storing program code which, when run on a computer, causes thecomputer to perform the method of operating a communications networkmanagement system adapted to store information describing the physicaland logical resources within a communications network, the networkcomprising a plurality of ports modelled according to a layer protocol,the method comprising the steps of: obtaining information describingconnectivity of ports in a first one of layers of the layer protocol;deriving further information concerning connectivity of ports in anotherof the layers; and using information concerning connectivity in thelayer protocol, in conjunction with information describing the physicaland logical resources within the network, to predict or infer networkservices available in client layers.
 17. A computer comprising aprocessing unit programmed to perform a method of managing acommunications network, the network comprising a plurality of portsmodelled according to a layer protocol and a network management systemadapted to store information describing the physical and logicalresources within the network, the method comprising the steps of:obtaining information describing connectivity of ports in a first one oflayers of the layer protocol; deriving further information concerningconnectivity of ports in another of the layers; and using informationconcerning connectivity in the layer protocol, in conjunction withinformation describing the physical and logical resources within thenetwork, to predict or infer network services available in clientlayers.
 18. A computer comprising a processing unit programmed toperform a method of operating a communications network management systemadapted to store information describing the physical and logicalresources within a communications network, the network comprising aplurality of ports modelled according to a layer protocol, the methodcomprising the steps of: obtaining information describing connectivityof ports in a first one of layers of the layer protocol; derivingfurther information concerning connectivity of ports in another of thelayers; and using information concerning connectivity in the layerprotocol, in conjunction with information describing the physical andlogical resources within the network, to predict or infer networkservices available in client layers.